The original security mechanism of IEEE 802.11 standard was not
designed to be strong and has proven to be insufficient for most net-
works that require some kind of security. Task group I (Security) of
IEEE 802.11 working group (http://www.ieee802.org/11/) has worked to
address the flaws of the base standard and has in practice completed
its work in May 2004. The IEEE 802.11i amendment to the IEEE 802.11
standard was approved in June 2004 and published in July 2004.
Wi-Fi Alliance (http://www.wi-fi.org/) used a draft version of the IEEE
802.11i work (draft 3.0) to define a subset of the security enhance-
ments that can be implemented with existing wlan hardware. This is
called Wi-Fi Protected Access<TM> (WPA). This has now become a manda-
tory component of interoperability testing and certification done by
Wi-Fi Alliance. Wi-Fi provides information about WPA at its web site
IEEE 802.11 standard defined wired equivalent privacy (WEP) algorithm
for protecting wireless networks. WEP uses RC4 with 40-bit keys, 24-bit
initialization vector (IV), and CRC32 to protect against packet
forgery. All these choices have proven to be insufficient: key space is
too small against current attacks, RC4 key scheduling is insufficient
(beginning of the pseudorandom stream should be skipped), IV space is
too small and IV reuse makes attacks easier, there is no replay protec-
tion, and non-keyed authentication does not protect against bit flip-
ping packet data.
WPA is an intermediate solution for the security issues. It uses Tempo-
ral Key Integrity Protocol (TKIP) to replace WEP. TKIP is a compromise
on strong security and possibility to use existing hardware. It still
uses RC4 for the encryption like WEP, but with per-packet RC4 keys. In
addition, it implements replay protection, keyed packet authentication
mechanism (Michael MIC).
Keys can be managed using two different mechanisms. WPA can either use
an external authentication server (e.g., RADIUS) and EAP just like IEEE
802.1X is using or pre-shared keys without need for additional servers.
Wi-Fi calls these "WPA-Enterprise" and "WPA-Personal", respectively.
Both mechanisms will generate a master session key for the Authentica-
tor (AP) and Supplicant (client station).
WPA implements a new key handshake (4-Way Handshake and Group Key Hand-
shake) for generating and exchanging data encryption keys between the
Authenticator and Supplicant. This handshake is also used to verify
that both Authenticator and Supplicant know the master session key.
These handshakes are identical regardless of the selected key manage-
ment mechanism (only the method for generating master session key
IEEE 802.11I / WPA2
The design for parts of IEEE 802.11i that were not included in WPA has
finished (May 2004) and this amendment to IEEE 802.11 was approved in
This program is licensed under the BSD license (the one with advertise-
ment clause removed).
16 October 2017 WPA_BACKGROUND(8)
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